By Jack Dash 

In a previous blog post we discussed some of the mushrooms commonly encountered in the Sonoran Desert. Mushrooms are the fruiting bodies of fungi (think of an apple on an apple tree) and are often visible above ground. But not all fungi produce visible mushrooms like macrofungi do. In this post we’ll dig a little deeper and discover what’s happening within our desert soils. Welcome to the fascinating world of mycorrhizal fungi! 

The word mycorrhizae comes from the Greek words for fungus (myco) and root (rhiza), and it describes a relationship between fungi and plants that is essential to the survival of both. Mycorrhizal fungi may not be as charismatic as macrofungi, in that they often don’t produce above-ground fruiting bodies. Yet they are some of the most important organisms in the desert. They form the foundation that supports all other lifeforms.

The “Desert Internet” 

Much ink has been spilled in recent years about the “wood-wide web,” the network of mycorrhizal fungi that grow underneath forest soils and connect the trees into an interdependent network of shared nutrients. However, much less attention has been given to this same network in desert ecosystems, where extreme conditions make mycorrhizal partnerships particularly valuable. Mycorrhizal fungi are fungus species that associate with the roots of plants in a mutualistic relationship that benefits both partners. Approximately 90% of the world’s plant species form mycorrhizal partnerships, demonstrating how essential fungi are to the health of all ecosystems—from forest to desert and pretty much everywhere in between. There are two main groups of mycorrhizal fungi that occur with our desert plants.  

• Ectomycorrhizal fungi (EC) are generally found on large trees and shrubs such as oaks and pines. EC attach themselves to the exterior of plant roots and form a mantle around them while sending out root-like structures called hyphae into the surrounding soil.  
• Vascular arbuscular mycorrhizae (VAC) colonize the inside of the plant’s roots, instead of surrounding the exterior. VAC is the most common form of mycorrhizal association, found in approximately 80% of mycorrhizal plant species and is by far the most common association type found in desert plants including cacti, grasses, and shrubs. These relationships are especially prominent in long-lived perennial plants and less common in annual or short-lived species who rely on producing seed quickly before dying. 

But wait—don’t fungi cause diseases in plants? A whole host of products exist to prevent plants from being colonized by pathogenic fungi, and you may hear harrowing tales of fungal infections. Why, then, do so many plants form these associations and what are the benefits? 

A Plantiful Partnership 

In essence, mycorrhizal associations are a form of resource exchange. Plants supply the fungi with carbohydrates produced by photosynthesis and the fungi provide the plants with water, nutrients, and greater resistance to diseases (sometimes from other fungi!) and unfavorable conditions. The hyphae of the fungi are smaller even than the smallest plant roots, allowing them to access tiny crevices in rock and radiate further out than the plant roots would be able to on their own. With the helping hands—er, strands—of hyphae, plants can access water they would not otherwise be able to reach. Meanwhile, the fungal organism obtains a source of energy that fuels their growth.  

Mycorrhizal fungi are also great at helping plants get the nutrients they need, especially those like phosphorus or iron that are typically found in limited quantities and often in forms that are difficult for plants to absorb. In addition to these bountiful benefits, mycorrhizal fungi also edge out pathogenic fungi that could cause harm to the plant as well as increase the plant’s tolerance to adverse conditions like saline soils. These characteristics make mycorrhizal fungi essential for desert plants by helping them thrive in inhospitable environments. 

Climate Change 

Mycorrhizal fungi are not just beneficial for plants. They also help improve the soil and stabilize the world’s climate! The hyphae of the fungi are wrapped in a thin layer of glomalin, a sticky substance made from the carbon acquired from their plant partners. As the hyphae get woody and are shed by the fungus, this glomalin stays in the soil for decades, effectively binding together soil particles to help prevent erosion and decrease dust in the air. Glomalin in the soil is also a carbon sink, storing massive amounts of carbon that would otherwise go up into the atmosphere and contribute to climate change. This is why it is damaging to disturb desert areas even where few plants are present—because you break up the binds that hold the soil together and release carbon.  

You may not see them, but mycorrhizae are always underfoot when you walk through the desert. They are quietly supporting our native vegetation, enhancing soil quality, and regulating climate change. These tiny organisms are the bedrock of our ecosystems and an essential part of the Sonoran Desert environment we know and love.  

Featured image by: Oyarte-Galvez (AMOLF) – CC BY-SA 4.0